Three Numbers, One Tradeoff

Every high-performance window is a balance of three NFRC metrics: U-Factor (heat loss), SHGC (solar heat gain), and VT (visible light transmittance). Optimizing one in isolation usually hurts another.

SHGC: Your Solar Control Lever

Solar Heat Gain Coefficient describes the fraction of solar radiation that enters through the window. In hot climates, low SHGC cuts cooling loads; in cold climates, moderate SHGC can offset heating by admitting free solar warmth.

VT: Light, View, and Glare

Visible Transmittance measures how much daylight passes through. High VT brightens interiors and reduces artificial lighting, but extremely high VT can also introduce glare and fading. The best glazing packages tune VT to the space’s orientation and function.

Reading the Combination

  • High SHGC + low U-Factor: ideal for heating-dominated, cold climates
  • Low SHGC + moderate U-Factor: ideal for cooling-dominated, hot climates
  • High VT + moderate SHGC: the “daylighting sweet spot” for mixed climates

VITRIUS publishes SHGC and VT for every glazing configuration—from the 80 Series Fixed (SHGC 0.261, VT 0.425) to the 127 Series Slim Casement (SHGC 0.179, VT 0.288)—so you can tune the envelope to your project, not the other way around.